Cobalt base alloy

ABSTRACT

Cobalt-tungsten alloys containing titanium, zirconium, carbon, chromium, rhenium, iron and nickel in preferred weight percentage ranges have superior strengths at elevated temperatures.

United States Patent 11 1 1111 3,762,918

Dreshfield et al. 1 Oct. 2, 1973 COBALT-BASE ALLOY 3,383,205 5/1968 Sims et al. 75/171 [75] Inventors: Robert L. Dreshfield, Middleburg 385 31196] giz 21: F Ohio; Gary Safldmck, 3,532,320 6/1971 Herchenroeder 75 171 Rmgwood, N.J.; John C. Freche, 3,432,294 3/1969 Wheaton 75/171 Fairview Park, Ohio [73] Assignee: The United States of America as represented by the Administrator of Primary ExaminerG. T. Ozaki the National Aeronautics and Space Att0rney-N. T. Musial et al. Administration, Washington, DC.

[22] Filed: Jan. 26, 1972 [21] Appl. No.: 221,093

[57] ABSTRACT [52] US. Cl. 75/170, 75/171 51 1m. (:1. C22c 19/00 Cwamungm? allcys f 581 Field of Search 75/170, 171 mm and nickel ferred weight percentage ranges have superior [56] References Cited strengths at elevated temperatures.

UNITED STATES PATENTS 3,276,865 10/1966 Freche et al 75/170 5 Claims, No Drawings COBALT-BASE ALLOY ORIGIN OF THE INVENTION The invention described herein was made by employees of the United States Government and may be manufactured and used by or for the Government for governmental purposes without the payment of any royalties thereon or therefor.

BACKGROUND OF THE INVENTION This invention is concerned with microstructurally stable, high-strength cobalt base alloys for use at elevated temperatures. The invention is particularly directed to cobalt-tungsten alloys for components in advanced gas turbines.

Nickel base alloys have been proposed for the hot components of gas turbine engines. However, many of the materials drop ofi sharply in strength above 1900 to 2000 F. Higher turbine inlet temperatures above 2000 F are necessary to meet the increased performance requirements of advanced gas turbines. This creates a need for materials that have improved strength at high temperatures.

While high temperature strength is of primary importance in gas turbines, ductility is also important at all temperatures to the maximum use temperature. The ductility must not be substantially decreased upon long time exposure at any temperature. A cobalt base alloy described in U.S. Pat. No. 3,276,865 has been considered for use in advanced gas turbines. However, this alloy is subject to embrittlement upon exposure to temperatures between 1200 F and 1600 F.

SUMMARY OF THE INVENTION OBJECTS OF THE INVENTION It is, therefore, an object of the present invention to provide cobalt-tungsten alloys having improved strengths at elevated temperatures up to 2125 F.

Another object of the invention is to provide microstructurally stable alloys having properties pertinent to long time engine applications.

A furtherobject of the invention is to provide a cohalt-tungsten alloy having adequate ductility at all temperatures to the maximum use temperature wherein the ductility is not substantially decreased upon long time exposure at any temperature.

These and other objects of the invention will be apparent from the specification that follows.

DESCRIPTION OF THE PREFERRED EMBODIMENT I The 5:25am invention is embodied in alloys having the following composition range, the amount of each alloying element being listed as a percentage by weight:

Percent Tungsten From about 10 to about 25 Titanium From about 0.5 to about 1 Zirconium From about 0.25 to about 0.5 Carbon From about 0.1 to about 1 Chromium From about to about Rhe'nium From about 0 to about 3 Iron From about 1 to about Nickel From about 1 to about 10 Cobalt Balance A preferred embodiment of the invention includes alloys having the following nominal composition range in weight percent:

Percent Tungsten From 15 to 20 Titanium From 0.5 to 1.0 Zirconium From 0.25 to 0.5 Carbon From 0.4 to 0.6 Chromium From 1 to 3 Rhenium From 2 to 3 Iron From 4 to 6 Nickel From 1 to 7.5 Cobalt Balance The alloys are prepared by conventional melting methods used for the preparation of either nickel-base or cobalt-base superalloys. Vacuum induction melting and investment castings are preferred for preparing cast parts.

Specimens of several known cobalt alloys and preferred compositions of the present invention were tested. A comparison of some mechanical properties of these specimens is shown in Table 1.

These test specimens were prepared by vacuum induction melting in stabilized zirconia crucibles. Before each melt was poured, the chamber was backfilled to 300 torr of argon. The pour temperature was determined by an optical pyrometer to be 3100 F. Zircon shell molds imbedded in tire-clay grog and held at 1600 F by a resistance mold heater were used.

Each casting consisted of a cluster of tensile test bars.

After casting, the molds were allowed to remain in the vacuum chamber for 15 minutes. They were then removed and permitted to cool to room temperature in about 6 hours before knock out and cutoff. Before testing all specimens were vapor-blasted and inspected by radiographic and fluorescent penetrant techniques.

An alloy described in U.S. Pat. No. 3,276,865 was vacuum melted and designated as VM 103. The nominal compositions of VM 103 and the other test specimens in weight percents are listed in Table 11.

TABLE II Alloy Co W Ti Zr Fe Re Ni Cr C VM 103 Bal 25.0 1.0 0.5 0 0 0 3.0 0.4 VM 105 Bal 20.0 1.0 0.5 5.0 3.0 0 3.0 0.5 VM 106 Bal 117.5 0.75 0.37 5.0 3.0 1.0 3.0 0.5 VM 107 Bal 20.0 1.0 0.5 5.0 3.0 0 3.0 0.6 VM 108 Bal 17.5 0.75 0.37 5.0 3.0 5.0 0.5 VM109 Ba] 17.5 0.75 0.37 5.0 3.0 7.5 3.0 0.5

The incipient melting temperature of VM 108, one of the preferred alloys, is between 2475 F and 2500 F.

This is 100 F higher than that of the highest melting point cast nickel base alloys. This is desirable for potential stator vane applications of advanced engines. These stator vanes must often withstand localized temperatures of 200 F or more higher than the average gas temperatures because of the uneven combustion gas profiles.

While several preferred alloys have been described, various modifications may be made to the alloy compositions without departing from the spirit of the invention or the scope of the subjoined claims. It is contemplated that the average electron vacancy concentration is controlled by suitable alloying adjustments to prevent formation of the intermetallic compound Co w which embrittles these alloys if it forms during exposure to temperatures between 1200 F and 1600 F.

What is claimed is:

1. A cobalttungsten alloy consisting essentially of in weight percents from 10 percent to 25 percent tungsten, from 0.5 percent to 1 percent titanium, from 0.1 percent to 1 percent carbon, from .25 percent to 0.5 percentz irconium, from percent to 5 percent chromium, from 0 percent to 3 percent rhenium, from 1 percent to percent iron, from 1 percent to 10 percent nickel, and the balance cobalt.

2. A cobalt-tungsten alloy as claimed in claim 1 consisting essentially of in weight percents from percent to 20 percent tungsten, from 0.5 percent to 1 percent titanium, from 0.4 percent to 0.6 percent carbon, from 0.25 percent to 0.5 percent zirconium, from 1 percent to 3 percent chromium, from 2 percent to 3 percent rhenium, from 4 percent to 6 percent iron, from 1 percent to 7.5 percent nickel, and the balance cobalt.

3. A cobalt-tungsten alloy as claimed in claim 1 consisting essentially of in weight percents from 17.5 percent to 20 percent tungsten, from 0.75 percent to 1 percent titanium, .5 percent carbon, from 0.37 percent to 0.5 percent zirconium, 3 percent chromium, 3 percent rhenium, 5 percent iron, from 1 percent to 7.5 percent nickel, and the balance cobalt.

4. A cobalt-tungsten alloy as claimed in claim 1 consisting essentially of in weight percents 17.5 percent tungsten, 0.75 percent titanium, 0.5 percent carbon, 0.37 percent zirconium, 3.0 percent chromium, 3 percent rhenium, 5 percent iron, from 5 percent to 7.5 percent nickel, and the balance cobalt.

5. A cobalt-tungsten alloy as claimed in claim 1 consisting essentially of in weight percents 17.5 percent tungsten, 0.75 percent titanium, 0.5 percent carbon, 0.37 percent zirconium, 3.0 percent chromium, 3 percent rhenium, 5 percent iron, 5 percent nickel, and the balance cobalt. 

2. A cobalt-tungsten alloy as claimed in claim 1 consisting essentially of in weight percents from 15 percent to 20 percent tungsten, from 0.5 percent to 1 percent titanium, from 0.4 percent to 0.6 percent carbon, from 0.25 percent to 0.5 percent zirconium, from 1 percent to 3 percent chromium, from 2 percent to 3 percent rhenium, from 4 percent to 6 percent iron, from 1 percent to 7.5 percent nickel, and the balance cobalt.
 3. A cobalt-tungsten alloy as claimed in claim 1 consisting essentially of in weight percents from 17.5 percent to 20 percent tungsten, from 0.75 percent to 1 percent titanium, .5 percent carbon, from 0.37 percent to 0.5 percent zirconium, 3 percent chromium, 3 percent rhenium, 5 percent iron, from 1 percent to 7.5 percent nickel, and the balance cobalt.
 4. A cobalt-tungsten alloy as claimed in claim 1 consisting essentially of in weight percents 17.5 percent tungsten, 0.75 percent titanium, 0.5 percent carbon, 0.37 percent zirconium, 3.0 percent chromium, 3 percent rhenium, 5 percent iron, from 5 percent to 7.5 percent nickel, and the balance cobalt.
 5. A cobalt-tungsten alloy as claimed in claim 1 consisting essentially of in weight percents 17.5 percent tungsten, 0.75 percent titanium, 0.5 percent carbon, 0.37 percent zirconium, 3.0 percent chromium, 3 percent rhenium, 5 percent iron, 5 percent nickel, and the balance cobalt. 